In the manufacture of vehicle wheel drop-center rims as now commercially produced, a strip of sheet metal stock cut to suitable width and length is coiled and the strip ends flash-butt-welded together to provide an annular element. The axial end portions of the annular element are flared outwardly in a flaring station and then the flared annular element is roll-formed in one or more roll-forming machines to provide a rim element having a rough drop-center rim contour and which is slightly diametrically undersize relative to rim final dimensions. The rolled rim element is then conveyed to a shaping apparatus, usually called an expander, in which the rim element is diametrically expanded by a segmental expansion die fixture to circumferentially stretch the material beyond its yield point to thereby impart a permanent set to the material at an enlarged finished diameter. Rim expander apparatus of this character is disclosed in Palmer U.S. Pat. No. 1,926,400 and in Yokomizo et al U.S. Pat. No. 5,010,759.
Such rim expanding apparatus is provided with radially movable shaping die segments arranged in a circular array and cooperating at their radially outermost surfaces to form an annular peripheral surface corresponding to the cross-sectional contour of the rim to be expanded. The die segments are moved from their innermost retracted positions radially outwardly into engagement with the rim to diametrically expand the rim a predetermined amount to circumferentially stretch and permanently set the rim material to thereby both accurately size and impart a true circular contour to the rim.
Such rim expanders developed for use with channel or drop-center wheel rims are typically provided with two sets of axially opposed segmental die fixtures adapted to be mounted one each on fixed and movable members of a horizontal or vertical axis press. The press mounted die fixtures are thus coaxially relatively movable and axially separable from one another to permit loading of a rim workpiece therebetween. The opposed fixtures are respectively inserted into the inboard and outboard ends of the rim and are closable together into abutment at a press parting line located by reference to the minimum inside diameter of the rim element to be worked. With this arrangement, the jaws or die segments need only have a short travel on their radial expansion working stroke despite the relatively large difference between the internal and external diameters of the typical drop-center rim. A short radial travel stroke of the die segments are important in reducing the amount of circumferential spacing between the individual sizing die segments of the segmental die in their fully expanded condition so as to minimize the rim "chording" phenomenon induced by the circumferential gaps between the expanded die segments.
The closed die set parting line location may be arranged to intersect the mid-point of the drop-center well, whereby each die set would engage the corresponding half of the rim well. More typically, however, one of the die sets is designed with its sizing die segments to engage the entire inner surface of an annular zone of the rim including one of the bead seats, an associated tire bead retaining flange and the drop-center well, and to abut the cooperating die set at a parting line located at the edge of the rim well remote from such bead seat. Hence this die set expands the drop-center well and one associated rim bead seat and flange, whereas the other opposed die set only expands the opposite bead seat and its associated flange.
In such known rim expanding apparatus, the two opposed segmental die sets may be individually expanded by two coaxially opposed and movable conical wedge expanding members, such as disclosed in the Bulgrin U.S. Pat. No. 3,706,120 (FIG. 8) and in the aforementioned Yokomizo et al U.S. Pat. No. 5,010,579 (FIGS. 4 and 5). However, it is preferred to use a single conical wedge expanding member for radially expanding both segmental die sets as disclosed in the Palmer U.S. Pat. No. 1,926,400, Bulgrin U.S. Pat. No. 3,706,120 (FIGS. 2-5) and Yokomizo et al U.S. Pat. No. 5,010,579 (FIGS. 1 and 2).
One well known and longstanding problem associated with such rim expanding apparatus is the prolonged set-up time required to accurately adjust each of the die segments of each of the segmental die sets. Typically each die segment is removably secured on a radially movable die holder of the die set to permit interchanging the same for expanding different types and sizes of rims. In order to accommodate such set-up changes as well as to make rim sizing adjustments to compensate for wear and stock thickness variations during a given production run, it has been necessary to individually disassemble and reassemble, either completely or partially, each die segment in order to manually insert properly selected shim stock between such segment and its associated holder to thereby adjust within precise tolerances the annular periphery presented by the die segment array to the rim. Inasmuch as each die set typically may contain as many as sixteen die segments, it often requires up to two hours or more for skilled set-up personnel to shim adjust the die set to change rim bead seat diameters (and thus the associated rim well diameter as a dependent variable). Obviously this is a costly procedure in terms of both labor and production line down-time.
Another problem with such prior rim expanding apparatus is that rim well inside diameter and either or both of the rim bead seat outside diameters are not independently adjustable relative to one another. Such dimensions of each of these three critical elements of the rim, as well as their roundness and concentricity relative to one another, are all well recognized as important quality control parameters which must be closely monitored in modern high speed mass production of wheel rims and disc assemblies. The inside diameter of the rim well must be closely controlled because, after the rim expansion station operation, the rounded and sized rim is conveyed to a disc assembly station where a wheel disc is telescopically press fit into the rim well. This rim and disc assembly is then conveyed to a subsequent station where the disc is welded to the rim. Hence, roundness and precise dimensional control of the rim well inner periphery are essential for optimizing the disc press-in production operation regardless of the roundness and diameter of the inboard and outboard bead seats of the rim.
On the other hand, it is also critical that each of the rim bead seats be finished to their outside diametrical dimensions within very close tolerances in a uniform manner. The bead seats also must be both round and concentric with one another as well as with the inner periphery of the rim well within very close tolerances.
Hitherto it has not been possible to independently control all three of these annular zones in the rim expanding operation because of the fixed relationship of the die segment surfaces in the one of the die fixtures which expands concurrently both the rim well and one of the rim bead seats. Accordingly, it has been difficult and costly in terms of set-up readjustment and production scrap rate to maintain the desired mass production uniformity with respect to the dimensional parameters of both the rim itself and the disc and rim wheel assembly in order to minimize radial run-out of the rim bead seats in the wheel assembly as well as disc-to-rim assembly defects.